Problem: $ { {4} \times \left[\begin{array}{r}{4} \\ {1} \\ {2}\end{array}\right] = {?} } $
Explanation: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{r}{4}\times{4} \\ {4}\times{1} \\ {4}\times{2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{16} \\ {4} \\ {8}\end{array}\right]}$